Smokers weigh less than nonsmokers, and typically gain 5-10 pounds upon quitting smoking, yet the mechanisms by which nicotine influences body weight remain unclear. Seventy-five smokers will be randomly assigned to one of three groups (stratified on the basis of a restrained eating score): 42 mg nicotine replacement, 21 mg nicotine replacement, or placebo. Subjects will receive transdermal therapy for eight weeks and intensive group counseling for sixteen weeks. Resting metabolic rate (RMR), thermic response to food, withdrawal ratings, three-day dietary records, nicotine/cotinine levels, and activity will be assessed in an overnight (twelve hour) calorimetry session prior to smoking cessation, and in 24-hour calorimetry sessions one, four, eight and sixteen weeks post-cessation. If the 42 mg nicotine dose is sufficient to maintain pre-smoking cessation set-point, at one and four weeks post-quit the 42 mg group should have a higher RMR and lower caloric intake than the other groups. The 21 mg group should weigh more than the 42 mg group by week 16. Decline in RMR should be strongly associated with increased withdrawal severity, and those subjects with restrained eating styles should show the greatest increases in caloric intake, weight, and decline in RMR. In addition to providing a powerful test of two theories (regulatory versus effector), this research also has great clinical significance. It may help to identify those smokers at greatest risk for weight gain, and suggest optimal strategies for managing weight gain related to smoking cessation. As fear of weight gain deters many smokers from attempting to quit, this information could provide significant health benefits.